This invention relates to the separation of gases by adsorption, and in particular to the adsorption separation of a feed gas from a crude gas, reacting the feed gas incompletely, adsorption separating product gas from feed gas, and recycling unreacted feed gas to the reaction stage.
Such a process has been known, for example, from DOS [German Unexamined Laid-Open Application] No. 2,610,227. This reference involves the production and recovery of ozone from a gaseous oxygen stream. The ozone is produced in a multistage ozone generator where oxygen atoms and oxygen molecules are combined. The energy required for splitting the oxygen molecules into atoms is supplied by electrical energy. The gaseous mixture withdrawn from the ozone-forming reaction contains several volume percent of ozone which represents the reaction product. The ozone-oxygen mixture is conducted to an adsorber station where the ozone content is preferably adsorbed, the adsorbent employed being preferably silica gel. Unadsorbed oxygen is recycled to the inlet of the ozone generator which is also charged with an oxygen content corresponding to the proportion of oxygen consumed during the ozone-forming reaction.
The feed oxygen, introduced continuously into the ozone generator, is obtained in a separate air fractionation plant which, for example, can be an adsorption plant. The desorption of the ozone separated in the adsorber station is effected with the aid of an inert scavenging gas, for example with the nitrogen obtained in the air fractionation plant. The air fractionation plant can be operated, if it is an adsorption plant, by using one of the conventional pressure swing processes.
The conventional process is highly oxygen-efficient since the unreacted oxygen from the ozone generator is constantly recycled, and only the proportion converted to ozone need be replaced by air fractionation. However, the process requires a large initial investment for the necessary apparatus. Thus, the system comprises an adsorber station for the separation of the ozone from the oxygen stream, as well as a separate air fractionation plant to obtain the oxygen. The considerable expenditure in apparatus must cover the adsorbent tanks proper as well as the associated control devices and fittings, noting that each of the two plants has at least two, and preferably three or four cyclically reversible adsorbent tanks.
In addition, assuming the adsorption of the components to be separated is conducted at low temperatures, as is often the case with adsorption processes, then, with two separate adsorption plants, there is also twice the expense for thermal insulation and for compensating for insulation losses.